1. Field of the Invention
The present invention relates to a lateral transient voltage suppressor, particularly to a lateral transient voltage suppressor with ultra low capacitance.
2. Description of the Related Art
Because the IC device sizes have been shrunk to nanometer scale, the consumer electronics, like the laptop and mobile devices, have been designed to be much smaller than ever. Without suitable protection devices, the functions of these electronics could be reset or even damaged under ESD (Electrostatic Discharge) events. Currently, all consumer electronics are expected to pass the ESD test requirement of IEC 61000-4-2 standard. TVS (Transient Voltage Suppressor) is generally designed to bypass the ESD energy, so that the electronic systems can be prevented from ESD damages. The working principle of TVS is shown in FIG. 1. In FIG. 1, the TVS devices 10 are connected in parallel with the protected circuits 12 on the PCB (Printed Circuit Board). These TVS devices 10 would be triggered immediately when the ESD event is occurred. In that way, each TVS device 10 can provide a superiorly low resistance path for discharging the transient ESD current, so that the energy of the ESD transient current can be bypassed by the TVS devices 10.
As shown in FIG. 2 and FIG. 3, the traditional TVS comprises a first diode 14, a second diode 16, and a zener diode 18. The first diode 14 is formed by a P-type heavily doped area 20, an N-type heavily doped area 22, and a P-type lightly doped well 24. The second diode 16 is formed by a P-type heavily doped area 26, an N-type heavily doped area 28, and an N-type lightly doped well 30. The zener diode 18 is formed by a P-type heavily doped area 32, two N-type heavily doped area 34 and 36, and a P-type doped well 38. Also, each doped well is isolated by a field oxide 40. However, after well drive-in process, the dosage of the P-type lightly doped well 24 and the N-type lightly doped well 30 will be still affected by the P-type doped well 38 and increased, which results in high input capacitance of the traditional TVS.
For high speed interface applications, such as Gigabit Ethernet, USB3.0 . . . , etc, the input capacitance of TVS should be designed as small as possible for better signal performance. However, the TVS device size should be designed large for better ESD performance which causes the large input capacitance. Therefore, how to reduce input capacitance of TVS device without reducing device size is a challenge.
To overcome the abovementioned problems, the present invention provides a lateral transient voltage suppressor with ultra low capacitance, so as to solve the afore-mentioned problems of the prior art.